This invention relates to improved types of seals for use in equipment in oil and gas wells and the like, and more particularly, to improved types of seals for sliding sleeve-type closures designed to maintain a sealing connection for relatively long time periods, such as the life of the well.
Sealing of components in oil and gas wells is of critical importance, both during the operation of downhole tools and for use in portions of the tools which remain in the well after completion, testing and production. For example, well apparatus with sliding closures frequently must be sealed during operation, and this sealing engagement must be maintained substantially indefinitely.
Prior art seals such as elastomeric seals can have problems over time in that the elastomer may lose resiliency or shape memory which is necessary for the seal to oppose the imposed forces thereon. This is a particular problem with exposure to downhole chemical and higher temperature environments of oil and gas wells for long periods of time. A seal is therefore required that remains operative in these types of environments.
Metal-to-metal seals have been developed because they are not affected by the chemicals and temperatures that are usually encountered. However, metal-to-metal seals are normally only used as static seals or as safety backup seals to standard elastomeric rotational or sliding seals because they have not been proven to be particularly suitable for use in dynamic sealing applications. One factor in the use of metal-to-metal seals is that the contacted sealing surfaces must be machined particularly smoothly and be free of pits and scratches so that a positive seal may be maintained. Damage to these surfaces can be caused by galling and scratching as the metal seal moves across the seal surface, and in such cases leakage is likely.
The present invention solves these problems by providing a new seal which incorporates the best aspects of metal-to-metal seals and elastomeric seals. In another embodiment, an improved metal-to-metal seal is also used to solve these problems.
Another type of prior art metal-to-metal seal is shown in U.S. Pat. No. 5,246,236. Such prior art metal-to-metal seal comprises a body portion disposable between the pair of members, a pair of annular arms extending from a side of the body portion, another pair of annular arms extending from an opposite side of the body portion, and a lip disposed on each of the arms adapted for engaging one of the members such that the first pair of arms are deflected toward one another and the second pair of arms are deflected toward one another. The two pairs of arms provide sealing in both directions. The arms are preferably integrally formed with the body portion.
In a preferred embodiment of such prior art metal-to-metal seal the apparatus further comprises elastomeric sealing means for dynamically sealing between the members as the members are relatively move. The body portion preferably defines a groove therein, and the dynamic sealing means is characterized by an elastomeric seal disposed in the groove.
One embodiment of such prior art metal-to-metal seal is characterized as a seal assembly for sealing between relatively movable first and second members, the first and second members defining a cavity therebetween. The seal assembly comprises a seal disposed in the cavity with a pusher ring disposed adjacent thereto. The seal comprises a body portion, a pair of annular arms extending from the body portion and defining a groove therebetween, and a lip on each of the arms. Each lip is adapted for sealing engagement with the sealing surfaces on one of the first and second members. The pusher ring has a portion extending therefrom into the groove such that longitudinal engagement by the lips with either of the first and second members is prevented.
The seal may further comprise a second pair of annular arms extending from an opposite side of the body portion from the first mentioned pair of arms, and a lip on each of the second pair of arms for sealing engagement wit-h the sealing surfaces of one of the first and second members. A second pusher ring is disposed on an opposite side of the seal and has a portion extending into the groove between the second pair of arms such that longitudinal engagement with the lips on the second pair of arms with the first and second members is prevented.
The seal assembly further comprises clamping means for clampingly engaging one of the pusher rings and thereby clamping the seal and the pusher rings to one of the first and second members.
Such prior art metal-to-metal seal further includes a sealed joint comprising a first member having a sealing surface defining first and second diameters, a second member having a sealing surface defining first and second diameters, the first and second diameters being relatively movable between first and second positions, and a seal defined between the first and second members. The seal comprises a body portion defining a groove therein, first and second annular arms extending from a side of the body portion and defining an annular groove therebetween, and third and fourth annular arms extending from an opposite side of the body portion from the first and second annular arms and defining an annular groove therebetween. First, second, third and fourth lips are disposed on the first, second, third and fourth arms, respectively. The first and third lips are spaced from the first diameter of the sealing surface of the first member when the first and second members are in the first position. The first and third lips are adapted for sealing engagement with the second diameter of the sealing surface of the first member when the first and second members are in the second position. The second and fourth lips are adapted for sealing engagement with the second diameter of the sealing surface of the second member. The seal in the seal joint further comprises an elastomeric sealing element disposed in the groove and adapted for sealing engagement with the first diameter of the sealing surface of the first member when the first and second members are in the first position and for tighter sealing engagement with the second diameter of the sealing surface of the first member when the first and second members are in the second position.
Yet other types of prior art seals having metal-to-metal sealing capabilities are illustrated in U.S. Pat. Nos. 2,470,925, 3,047,300, 3,288,222, 4,131,287, 3,915,462, 4,178,020, 4,452,462, 4,474,382, 4,766,956, 4,471,965, 4,477,085, 4,478,423, 4,787,642, 4,815,770, 4,823,871, and 5,044,672. Still yet other types of prior art seals having elastomeric seals, elastomeric and metal-to-metal seals or metal-to-metal seals are illustrated in U.S. Pat. Nos. 3,387,656, 3,387,661, 3,489,098, 3,599,490, 4,315,543, 4,477,091, 4,510,960, 4,613,159 and 4,796,858.
Also, metal-to-metal seals in downhole completion equipment are discussed in an October 1990 issued of the Journal of Petroleum Technology in an article entitled "Metallic Sealing Technology in Downhole Completion Equipment" by William A. Blizzard.